Preheat the oven to 180°/ 425ºF and spray a large baking tray with olive oil.
Heat the olive oil in a large pan over medium heat. Add the capsicum and onion; cook for 5 to 6 minutes, until soft.
Add black beans, tomatoes, spinach, taco seasoning, and the reserved black bean liquid. Use a potato masher or the back of a wooden spoon to partially mash about half of the black beans. Simmer for 2 to 3 minutes, until the mixture thickens.
Place tortillas on a plate and cover with a damp paper towel. Microwave for 30 seconds, until tortillas are warm and pliable.
Arrange the tortillas on the baking tray. Sprinkle half of each tortilla with a little cheese, followed by 2-3 tablespoons of the black bean mixture. Top with another light sprinkle of cheese, and fold over the tortilla; press to adhere. Repeat with the remaining tortillas.
Bake for 10 to 15 minutes or until golden, flipping halfway. Serve with the avocado crema on the side.
