Deep Rock Galactic

The fastest way to find two Dreadnoughts in a row on is to run a Elimination Mission, as the goal in Elimination Missions is specifically to destroy Dreadnoughts. Obviously, running as Hazard Level 3 mission is the best, as the challenge becomes more difficult on levels 4 and 5. Best if done in a group as well, as one person can distract the Dreadnaughts while the others shoot at its weak spot.

In Elimination Missions, Dreadnaughts will be inside cocoons, which means you can take your time in finding two cocoons before starting this challenge (the cocoons themselves appear on the scanner as bright red egg shapes) Just be careful not to damage the cocoon until you're ready to begin the fight, as they damage and open very easily.

You'll know you're fighting a Dreadnaught as it is the rare enemy that has a health bar visible at all times at the top of the screen. Dreadnaughts cannot be damaged normally, only through its weak spot, which is behind it. Unlike most bugs in the game however, there are armored shells covering the weak spot you need to shoot off first before being able to hit the weak spot. The armored shells will regenerate over time if the Dreadnaught isn't shot up enough, so keep that in mind.

In summary, find two cocoons, start a fight at one, then when its over run as quickly as you can to the second one and start that fight. Five minutes should be plenty of time for two Dreadnaughts with a decent team on Hazard Level 3.