Bring a large pot of lightly salted water to a boil. Cook elbow macaroni in the boiling water, stirring occasionally until tender yet firm to the bite, 8 minutes. Drain and transfer to a 9x13-inch casserole dish.
Preheat oven to 350 degrees F (175 degrees C).
Blend tofu in a food processor until smooth, about 2 minutes. Add Swiss cheese, Greek yogurt, and Dijon mustard; mix well to combine.
Heat oil in a large skillet over medium-high heat. Add mushrooms, spinach, green bell pepper, onion, and garlic; saute until tender, about 5 minutes. Stir tofu mixture into the skillet. Cook until flavors combine, 2 to 3 minutes. Season with salt and ground black pepper.
Spoon tofu and mushroom mixture over macaroni in the casserole dish; mix to combine. Cover with aluminum foil.
Bake in the preheated oven until bubbly and golden, about 30 minutes.