Slice the zucchini and yellow squash into 1/2-inch thick rounds—this thickness is crucial as it allows the vegetables to develop a golden exterior while staying tender inside. In a large bowl, combine the olive oil, Italian seasoning, garlic powder, salt, black pepper, and red pepper flakes. Add the sliced vegetables to the bowl and toss gently but thoroughly until every piece is evenly coated with the seasoned oil. I like to use my hands for this step rather than a spoon, as it ensures better coating and helps you feel if any pieces are missing the oil.

Preheat your oven to 425°F. Spread the seasoned vegetables from Step 1 on a baking sheet in a single layer, making sure they're not overlapping or crowded—this allows hot air to circulate around each piece and creates better browning. Roast for 10-12 minutes until the vegetables are tender and beginning to show light golden color on the edges. For a crispier result with more caramelization, proceed to the broil step; otherwise, transfer to a serving dish.

If desired, switch your oven to broil and return the roasted vegetables for 3-6 minutes, watching carefully to prevent burning. The broiler will create darker, caramelized spots and deepen the flavors. I recommend moving the pan to the lower rack before broiling so the vegetables caramelize rather than char. Once done, transfer to a serving dish and immediately sprinkle with the freshly grated Parmesan cheese while the vegetables are still hot—this helps it melt slightly and adhere to the pieces.