Prep the pan and oven. Heat the oven to 350°F (175°C).
Lightly grease a mini muffin tin with olive oil or nonstick spray, making sure to coat the sides so the eggs release easily.
Whisk the eggs. In a medium bowl, whisk eggs and milk until smooth and slightly frothy. This helps create a fluffier texture kids enjoy.
Season gently. Add cumin, mild chili powder, salt, and a pinch of black pepper. Keep the seasoning light for little palates.
Stir to combine.
Add the mix-ins. Fold in bell pepper, black beans, corn, green onions, and shredded cheese. Stir just until everything is evenly distributed.
Fill the cups. Spoon the mixture into the mini muffin cups, filling each about 3/4 full. Give the pan a small tap on the counter to settle the ingredients.
Bake. Place the pan on the middle rack and bake for 12–15 minutes, or until the centers are set and a toothpick comes out clean.
The tops should look puffed and slightly golden around the edges.
Cool briefly. Let the muffins rest in the pan for 3–4 minutes. Run a small offset spatula or butter knife around the edges and lift them out gently.
Serve. Offer with mild salsa, diced avocado, or a dollop of plain Greek yogurt. For very young kids, serve plain or with a tiny smear of yogurt for creaminess.