Roughly chop the shrimp into quarter-inch pieces. Season with garlic powder, salt, and pepper.
Wash and chop the mushrooms and tomatoes. Preheat the olive oil in a skillet over medium-high heat until shimmering. Add the mushrooms and tomatoes, and sauté until the mushrooms have lost their moisture, about 5-7 minutes.
Add the spinach to the skillet and gently stir until wilted. Let any excess moisture evaporate, then remove from the heat.
Spread the spinach mixture in an even layer over the sirloin. Place the seasoned shrimp on top. Roll the sirloin around the shrimp and spinach into a pinwheel shape. Secure with toothpicks, then cut into individual portions, about 2 inches thick.
Sear the pinwheels on each side for 4-5 minutes or until the beef is no longer pink and the shrimp are cooked thoroughly. Serve immediately. Enjoy!