Adjust rack to top position (top and middle positions for 8 servings) and preheat oven to 425 degrees. Wash and dry produce.

Drain and rinse beans. Trim and discard root end from lettuce; thinly slice leaves into shreds. Dice tomatoes into ¼-inch pieces.

Heat a drizzle of oil in a large pan over medium-high heat. Add beef*, garlic powder, salt, and pepper. Cook, breaking up meat into pieces, until browned and cooked through, 4-6 minutes.

In the last 2 minutes of cooking, add beans; stir until warmed through.

Transfer beef and bean filling to a plate.

Lay tortillas on a clean work surface. Evenly spread bottom half of tortillas with half the cheddar and half the white cheddar. Top with beef and bean filling, then top with remaining cheese. Fold tortillas in half to create quesadillas.

Place quesadillas on a lightly oiled baking sheet and drizzle tops with oil. Bake on top rack until tortillas are crisped and cheese melts, 15-20 minutes, flipping halfway through. (For 8 servings, divide between two baking sheets; bake on top and middle racks.)

While quesadillas bake, in a small bowl, combine ketchup and mayonnaise. 

Place lettuce and tomatoes in a large bowl. Add dressing; season with salt and pepper. Toss to combine.

Cut quesadillas into wedges and divide between plates. Serve with salad and special sauce on the side.