Pre-heat oven to 180 degrees Celcius. Prepare a 6 cup muffin tray by greasing it well.
In a pan heat 1 tbsp oil. Add chopped Garlic. Followed by chopped onion. Fry till the onion looks soft and cooked. Add Chopped tomatoes. Cook the tomatoes are cooked for about 2-3 minutes.
Add chopped red bell pepper. Slightly crush the bean and corn using a potato masher/fork/by hand. Add to the pan. Mix well.
Add salt, cumin powder, cinnamon powder, and chili powder. Fry until everything is cooked through and comes together. Add chopped coriander. Sprinkle Mexican seasoning if using. Switch off the gas and let the mixture cool.
Meanwhile, crack the egg in a mixing bowl. Add milk. Season with salt and pepper. (Keeping in mind the above-cooked mixture has already salt and chili in it).
Divide the egg mixture equally among 6 muffin cups. Spoon the above-cooked mixture equally into the cups. Sprinkle shredded cheese on top (if using). (It's ok if the cups are almost full. The mixture will not spill once it is baked)
Bake for 8-10 minutes. (The muffins will rise and look puffy when in the oven but they will shrink back once cooled down).
Serve warm. (If serving later heat it for 10 -15 seconds in Microwave before serving)