Set your oven on broil. Toss chopped summer squash with olive oil, garlic salt, paprika, crushed red pepper flakes, and herbs de provence. Evenly distribute the seasoned squash on a large baking sheet and place on the middle rack. Let the squash broil for about 20-30 minutes or they're tender and golden brown. Remove from heat and set in a strainer to remove excess liquid. This step can be made a few days in advance.
Preheat oven to 350 degrees. Whisk together eggs, sour cream, salt and pepper until mixture is smooth and set aside. Spray the inside of your baking dish with nonstick spray and evenly add the cooked summer squash, the caramelized onions, and half the dill. Carefully pour the whisked egg mixture on top - just enough that the top of veggies are just barely covered - and sprinkle the goat cheese on top.
Next, bake for 35-45 minutes or until the sides of the frittata are lifted from the edges and the center is cooked through. Not sure if it's done? Carefully wiggle the middle of the frittata with a spoon and if it seems mushy, leave it in for longer. This isn't an exact science but just make sure the eggs are cooked through Before serving, add the rest of the dill on top for garnish.