1. Wash and dry all the vegetables, then cut the broccoli, peppers, mushrooms, and onion into even pieces for consistent cooking.

2. Heat the olive oil in a large skillet over medium to medium-high heat, then add the onion and cook until it begins to soften.

3. Add the broccoli and sauté for a few minutes until it turns bright green and starts to become tender-crisp.

4. Stir in the bell peppers and mushrooms, then cook until the mushrooms release their moisture and the peppers soften slightly while still keeping some bite.

5. Add the garlic, Italian seasoning, crushed red pepper flakes, salt, and black pepper, then stir for about 1 minute until fragrant.

6. Finish with the butter, lemon juice, and fresh parsley, then toss everything together and serve warm.