Preheat grill or grill pan to medium-high heat.
Toss the zucchini, squash, tomatoes, onion, and bell pepper with the olive oil, salt, oregano, garlic powder, and thyme in a large mixing bowl.
Thread the vegetables onto skewers.
Place them on the grill and cook them for 3 to 5 minutes or until grill lines have formed. Flip them over and grill for another 3 to 5 minutes until charred. Remove immediately and place on a large plate or cutting board. Allow vegetables to cool for 1 to 2 minutes.
Remove the vegetables from the skewers. Drizzle the lemon juice over the top. Top with optional parsley, if using. Serve immediately.