Preheat oven to 350°F (180°C). Line a 12-cup muffin pan with parchment paper liners; set aside.
In a small non-stick skillet, over medium heat, combine onion, garlic and oil. Cook, stirring occasionally, until softened, about 4 minutes. Remove from heat. Stir in carrot, corn, salt and pepper. Spoon vegetable mixture evenly into prepared muffin pan and sprinkle each muffin cup with 1 tbsp (15 mL) of cheese.
In a large bowl, whisk eggs, salt and pepper until combined. Pour evenly into muffin cups. (You may have a bit of egg mixture left over; resist the urge to overfill.)
Bake for 20 to 25 minutes or until frittatas are set in the centre and puffed. Sprinkle each with remaining cheese and jalapeño (if using). Let cool in pan on a wire rack for 5 minutes.
Tip: Kick up the heat by topping your frittata with salsa or sriracha mayo.