Preheat oven to 450°F. Heat grape-seed oil in heavy large pot over medium-high heat. Add chopped bacon and cook until fat is rendered, about 6 minutes. Using slotted spoon, transfer bacon to paper towels and drain. Set aside.
Sprinkle chicken sausage pieces. Add chicken sausage to bacon drippings in pot and cook over medium heat until brown, about 7 minutes per side. Using tongs, remove chicken sausage from pot.
Add chopped onions and garlic to pot and saut until beginning to brown, scraping up any browned bits, about 10 minutes. Stir in rice, roasted pimientos(I usually use olives) with juices and saffron. Add clam juice and chicken stock to pot and bring mixture to simmer. Remove from heat.
Pour rice mixture into 15x10x2-inch glass baking dish. Arrange chicken sausage, shrimp and clams in rice mixture. Sprinkle with chopped bacon and peas. Cover with foil.
Bake paella until chicken sausage is cooked through and clams open and rice is tender, about 45 minutes (discard any clams and mussels that do not open). Remove foil from baking dish. Let paella stand 10 minutes. Serve with lemon wedges.