Start by placing the chicken tenders and shrimp into a large resealable bag. Whisk together olive oil, Italian seasoning, minced garlic, freshly ground pepper, and salt in a small bowl, then pour the mixture over the chicken and shrimp. Seal the bag and let it marinate in the refrigerator for at least 4 hours to absorb all the flavors.
Meanwhile, bring a large pot of salted water to a rolling boil and cook the spaghetti until al dente according to the package instructions. Drain well and set the pasta aside.
While the pasta is cooking, heat a large skillet over medium-high heat and add the marinated chicken, shrimp, and remaining marinade. Sauté for about 7 minutes, then toss in the thinly sliced red bell peppers and cook for an additional 5 minutes. Remove from heat and set aside.
In the large pot used for the pasta, add a tablespoon of olive oil and warm it over medium-high heat. Stir in the diced pancetta and cook for roughly 5 minutes, stirring frequently, until the pancetta is crisped and browned.
Lower the heat to medium-low and mix the salted butter into the pot until melted. Quickly whisk in the flour to form a roux, then add crushed garlic, grated parmesan cheese, heavy cream, and egg yolks. Continuously whisk this mixture for 5 minutes to thicken the sauce while preventing the eggs from scrambling.
Fold in the cooked spaghetti to coat with the creamy carbonara sauce thoroughly. Transfer the pasta into a 9x13-inch baking dish, spreading it evenly. Layer the sautéed chicken, shrimp, and bell peppers on top.
Preheat your oven's broiler to a low setting for gentle browning. In a small bowl, combine parmesan romano cheese, shredded mozzarella, Italian-seasoned panko breadcrumbs, melted butter, and garlic powder until well mixed. Evenly sprinkle this topping over the pasta and seafood layer.
Place the baking dish under the broiler and cook for 5 to 7 minutes, watching closely until the topping turns golden brown and crispy.
Remove the casserole from the oven and scatter freshly chopped parsley over the top for a fresh finish. Serve the dish warm and enjoy a flavorful copycat Olive Garden classic.