Onto each skewer, alternately thread green bell pepper chunks, shrimp, zucchini slices, chicken, cherry tomatoes, steak, onion, mushroom; repeat until skewer is full. Drizzle olive oil over the prepared skewers; season with 1/4 teaspoon garlic powder, salt, and black pepper. Allow to marinate in refrigerator at least 3 hours, turning every 45 minutes.
Preheat an outdoor grill for medium-high heat, and lightly oil the grate.
Bring a pot of lightly salted water to a rolling boil. Cook the fettuccini in the boiling water, stirring occasionally, until cooked through yet firm to the bite, about 8 minutes; drain. Toss the hot pasta in a large bowl with the softened butter and 1/4 teaspoon garlic powder.
While the pasta boils, cook the skewers on the preheated grill, turning frequently until nicely browned on all sides, the shrimp are pink and opaque, and the meat is no longer pink in the center, 10 to 15 minutes. Push the cooked meat and vegetables off the skewer onto the tossed pasta.