In a small bowl, combine chili powder, cumin, paprika, garlic, 1 teaspoon salt and 1/2 teaspoon pepper. Season steak with chili powder mixture.
Brush steak with 1 tablespoon canola oil. Add steak to grill, and cook, flipping once, until desired doneness, about 4-5 minutes per side for medium-rare. Let rest 5 minutes.
Season bell peppers and onion with remaining 1 1/2 tablespoons canola oil; season with salt and pepper, to taste.
Add bell peppers and onion to grill, and cook, turning occasionally, until charred and tender, about 6-8 minutes.
Thinly slice steak against the grain and serve with bell peppers and onion.
To make the fajita mix, take two or three strips from each colour of pepper and finely chop them. Set aside. Heat the oil in a frying pan and fry the remaining pepper strips and the onion until soft and starting to brown at the edges. Cool slightly and mix in the chopped raw peppers. Add the garlic and cook for 1 min, then add the spices and stir. Cook for a couple of mins more until the spices become aromatic, then add half the lime juice and season. Transfer to a dish, leaving any juices behind, and keep warm.
Tip the black beans into the same pan, then add the remaining lime juice and plenty of seasoning. Stir the beans around the pan to warm them through and help them absorb any flavours of the fajita mix, then stir through the coriander.
Warm the tortillas in a microwave or a low oven, then wrap them so they don’t dry out. Serve the tortillas with the fajita mix, beans, avocado and soured cream for everyone to help themselves.
