I have made vegetarian fajitas using chestnut mushrooms, onions, garlic, red, green, and orange peppers. I serve it with tortillas, salsa, refried beans, sour cream, grated cheese, cilantro, pico de gallo (chopped onion, tomatoes and cilantro), and guacamole.
For the fajita seasoning
2 teaspoons ground cumin
1 teaspoon ground coriander
1/4 teaspoon dried oregano
Salt
Black pepper
1.5 teaspoon smoked paprika
Cayenne pepper
I add the juice of a lime before serving.
Or you can cheat and use the smoked BBQ fajita packs from Aldi which are excellent.
Aldi also do a very good Thai green curry kit which I use the same vegetable mixture to. Their Thai red curry kit makes a good base for massaman, I just add a potato to the vegetable mixture, 1 teaspoon brown sugar, 1 teaspoon cinnamon, 1/4 teaspoon cardamon, 1 teaspoon ground cumin, 1/2 teaspoon ground coriander, 1 tablespoon smooth peanut butter.