Preheat an outdoor grill to medium-high heat until it reaches approximately 350°F. Place bamboo skewers in a shallow pan filled with warm water and soak for 30 minutes.
Rinse 1.5 pounds raw shrimp and pat dry with paper towels.
In a large mixing bowl, whisk together ¼ cup olive oil, the juice of 1 lemon, 1 teaspoon Italian seasoning, ½ teaspoon garlic powder, ½ teaspoon salt, and 1 teaspoon red pepper flakes.
Add 1.5 pounds shrimp, 1 red bell pepper cut into large pieces, 1 zucchini cut into large pieces, 1 yellow squash cut into large pieces, and 1 red onion cut into large pieces to the marinade. Toss until the shrimp and vegetables are evenly coated. Cover and refrigerate for at least 30 minutes.
Thread the shrimp and veggies onto the skewers. Repeat until all ingredients are used.
Grill for 3-5 minutes on each each side until the shrimp is cooked through and the veggies are the tenderness that you prefer.
Serve immediately.
Notes
Refrigerate the leftovers in an air tight container for up to 3 days.