Enchilada Sauce: Combine all ingredients in a pan. Bring to a boil, then reduce to a simmer and cook for about 5 minutes.
Vegan Enchilada Grilled Cheese: Pour olive oil in a hot pan and add chopped onions. Cook until translucent.
Add chopped red pepper and cook until slightly tender.
Add sliced mushrooms and cook until tender. Add salt and pepper.
Add 2 tablespoons of enchilada sauce and cook a couple of minutes more.
Spread about ½ a teaspoon of vegan mayo on each slice of bread. This will be the outside of the sandwich because you're cooking them in the vegan mayo.
Place ¼ of red pepper mushroom mixture each on four slices of bread. Place vegan cheddar on top of mixture. Add a drizzle of enchilada sauce on top.
Place a sandwich on a hot pan. Dome the sandwich with a frying pan lid or metal mixing bowl. Optional: Sprinkle a little water in the pan. This technique helps to melt the vegan cheese faster.
Cook until golden brown. Flip, and cook the other side. Repeat with the rest of the sandwiches.