In a medium bowl combined black beans, cilantro, lime zest, lime juice, and red pepper flakes.
Taste and adjust salt and pepper.
Warm tortillas in a pan or on a gas burner until flexible and pliable.
One tortilla at a time, add 3/4 cup black bean mixture, 1 tbsp onion and a handful halved tomatoes.
Top with 1/4 avocado, sliced. Repeat with remaining tortillas.
Wrap by first folding the left and right sides in, then folding the bottom flap up and rolling the burrito up until all flaps and seams are on the bottom.