Add the milk, eggs, mustard, thyme, and romano cheese to a medium sized mixing bowl. Using a hand mixer, whisk together on low speed until evenly combined & frothy.
To a large mixing bowl add the flour, baking powder, salt, and pepper. Using a fork, whisk them together until evenly combined. Set aside.
Add the zucchini & corn to the bowl, gently tossing to until evenly mixed.
Reserve a few tomato pieces, for topping the muffins, and add the rest to the mixing bowl. Stir gently to evenly combine and coat in the flour mixture.
Pour the wet mixture into the bowl of combined dry ingredients. Using a spatula, stir just until combined. Fold in a 1/2 cup of the feta cheese, but don't overmix.
Generously spray a muffin tin with non stick cooking spray to coat the wells. Spoon the batter in the prepared pan.
Top each with a couple pieces of tomato and feta, then bake the muffins at 400° for 20-22 minutes, or until all the muffins are puffed up and golden brown on top.
Remove the muffins from the oven, and allow them to rest for a full 5 minutes.
Run a butter knife around the edges of each to release them from the pan and then transfer them to a wire rack to finish cooling.
Serve the muffins as is, or with softened butter, and enjoy!