Preheat the oven to 425°F/220°C/Gas Mark 7 (if you have a fan option or a convection oven, bake the vegetables on two baking trays at 400°F/200°C).
Prepare the vegetables: Peel the sweet potato and cut into 3/4-inch (2cm) cubes. Cut the bell pepper into 3/4-inch (2cm) cubes. Peel the onion and cut into 1/4-inch (5mm) slices. Toss the vegetables with olive oil and fajita seasoning, season to taste with salt and pepper. Distribute evenly on a baking sheet. Make sure the vegetables are not overcrowded or they won't brown properly - it's better to bake them in two batches. Bake them for about 20 minutes - they should be soft and nicely browned.
Melt the butter in a small pot, add pressed garlic cloves and cook for 30 seconds, stirring. Take the pot off the heat and add the lemon juice.
Add the drained corn, beans, and shredded on the large holes of a box grater cheese into a very large bowl. Stir everything together.
When the vegetables are done, pour the butter-garlic-lemon mixture over them, toss with the liquid, then transfer to the bowl. Scrape with a wooden spatula all the brown bits at the bottom of the baking sheet, add them to the bowl.
Season the filling with salt and pepper, stir everything together.
Place 2-3 heaped tablespoons filling over a half of a large tortilla (leaving some border so that the filling won't fall out when frying), then fold it in half.
Heat 2 tablespoons of oil in a large frying pan. Add two fold in half tortillas. Cook over medium heat on both sides until the tortilla is golden and the cheese is melted (when adding tortilla to a pan, move with them to make sure they are not sticking to the pan). Transfer to a plate, sprinkle the tortilla lightly with salt. Repeat with the remaining tortillas.
Cut into triangles (cut each tortilla into 2 or 4 parts) and serve with yogurt dip (mix the yogurt with lemon juice, pressed garlic clove, and season with salt and pepper).
Enjoy!