Pre heat your oven to 350 degrees F.
Grate the Zucchini and then wrap in paper towels and squeeze out a lot of the moisture
Heat the olive oil in a Large deep skillet or saute pan (that is oven safe) over medium heat
Warm the garlic in the oil
Saute the onion, basil, potatoes, and zucchini in the pan up on medium high heat until the mix turns golden brown
Add the milk, eggs, and black pepper to a blender and blend on the highest speed until frothy.
Pour the egg mixture over the ingredients in the pan.
Let it set for one minute on the stove top.
Add the cheese, float the tomato slices on top and finish the frittata in the oven for ten minutes and the eggs have cooked through.
Slice and serve.