Preheat oven to 350 degrees F.
Bring a large pot of water to a boil, add pasta and cook according to package directions for al dente; drain and set aside.
In a large skillet or pan, heat olive oil over medium-high heat.
Add ground turkey, diced onion, minced garlic and steak seasoning to the pan and cook until turkey is browned; drain any excess liquid.
Add undrained cans of diced tomatoes, tomato paste, mustard, pickle relish, 1/2 cup cheddar cheese and sour cream.
Reduce heat to medium and stir continuously until it starts bubbling.
Add mixture to cooked Penne pasta and mix until well combined.
Pour mixture into a 9 x 13 inch baking dish sprayed with nonstick cooking spray.
Top with remaining 1/2 cup cheese.
Bake for 20-25 minutes or until cheese is melted and casserole is completely heated through.
Top with shredded lettuce and diced tomatoes before serving.