Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 450 degrees. Wash and dry produce.
Quarter lime. Halve, core, and thinly slice green pepper into strips. Halve, peel, and thinly slice onion. Drain and rinse beans. Roughly chop cilantro.
In a small bowl, combine sour cream with a squeeze of lime juice. Season with salt and pepper. Stir in water 1 tsp at a time until mixture reaches a drizzling consistency.
Heat a drizzle of oil in a large pan over medium-high heat. Add beef or turkey; season with salt and pepper. Cook, breaking up meat into pieces, until lightly browned, 3-5 minutes (it will cook through in Step 5). Turn off heat; transfer to a plate. Carefully discard any excess grease from pan if necessary. Wipe out pan.