Sunset Overdrive

This achievement entails completing 3 side quests (blue !)
- Fizzco: The Dirty Secret
- Fizzco: The International Conspiracy
- Fizzco: The Secret Ingredient

The latter are started at a phone booth but I believe the first is started by reading a note at the base.
You need to progress through the story to unlock these missions, the third of which is unlocked sometime during when you are getting the 4th faction to help you (the Latino ninja cheerleaders).

My main difficulty with this achievement was finding the side quests, so I decided to write the solution I would have liked to have when searching for info on this achievement.

I did this after completing all main quests, so except for the first one, I can't confirm the earliest time that they become available.

You can see the names of the areas in the map by hovering the pointer over the fast travel (orange) arrows in each area.

So, as both other solutions mention, to unlock this achievement you need to finish three side quests (marked with blue exclamation marks on the map). The first of these three quests, Fizzco: The Dirty Secret, is available at the Diner Fort, on a pay phone that is to the right of where Floyd is (if facing Floyd). When you approach it, you get the prompt to read the note and complete the side quest (you can leave it for later if you prefer; if you do so, it will be available on the quests list on the menu).

So you read the note on the phone booth at the Diner Fort and you are asked to find a payphone at the park. Once you get there, you have to pick up the phone and are given the new objective of finding the first recycling truck, where there's supposed to be some evidence against Fizzco. You get there, search the truck (by pressing Y) and when doing that you are attacked by Fizzco Agents. You have to kill all of them to be able to open the truck. Once you kill them, you get the new objective of collecting the memos from the truck (1/3 memos). Then you have to go to the second truck (Old Factory District, the location will be marked with a waypoint), and you'll have to repeat the process (search the truck, defeat the Fizzco Agents that appear, collect the memo). That would be memo 2/3. Rinse and repeat for the third recycling truck & memo 3/3 (also in the Old Factory District). When you have all three memos, you have to go to a drop-off location indicated by a waypoint and drop off the evidence.

(Credit for the video to YouTube user Joey Houlahan)

Once you complete the first quest, the second one (Fizzco: The International Conspiracy) becomes available.

This side-quest will be marked on the map after you finish the first one. You will find it on a ringing payphone near the Harbor Fort, outside the fort to one of the sides (left if you're facing the water). You'll be instructed to collect the contents of eight biohazard crates. These will be located in blue areas that you will have to search to find the evidence (and of course, enemies will spawn there, but you don't necessarily have to kill them to be able to collect the evidence). Once you've collected all eight crates, you'll have to go to the drop-off location to finish the mission.

I was able to find a video on YouTube for this one that shows the location on the map (bottom left at the very beginning of the video):

(Credit for the video to YouTube user XboxOneGaming)

After completing the second quest, the third one (Fizzco: The Secret Ingredient) becomes available. A mark will appear on the southern part of the Downtown area of the map (which is the uppermost part of the entire map). This is the third and final side-quest you have to complete for the achievement. Again, a phone will be ringing and you'll be prompted to pick it up. You'll be instructed to clean out the OD and Gunk in the Water Treatment Plant. The Gunk are big chunks of some sort of material that are stuck to pipes (there's 6 pieces of gunk in total). When you destroy them all by shooting them, you have to transfer the data from the computer (it will be marked on your map, it's in the area you just cleaned up). When you log into the computer, Fizzco Agents arrive and you have to fight them off for 60 seconds while the data transfers. After that, you have to go to the computer and download the data. Something happens (not saying what, it would be a spoiler) and then you have to fight Fizzco Bots. Do that and get your achievement.

(Credit for the video to YouTube user Joey Houlahan)