Heat up your grill to medium - medium high heat.
Prepare your vegetables: slice the zucchini and summer squash vertically into 1/8 - 1/4 inch thick. Slice the bell pepper and red onion into quarters. Brush both sides of the vegetables with olive oil.
Grill the veggies about 5 minutes per side, or until it become slightly opaque with brown grill marks.
Remove from the grill, and slice into small pieces, about 1/2 inch pieces.
Place about 1/3 cup veggies, 1/4 cup black beans, and a few tbsp of cojita cheese into each tortilla.
Place filled tortillas back on the grill. Grill for additional 3-4 minutes per side, or until cheese is melted.
Serve with avocado, salsa, sour cream, or any other toppings.