Preheat the oven to 425 degrees F. Line a baking sheet with foil; set aside. Place the acorn squash in a microwave-safe bowl with 1/4 cup water. Loosely cover with plastic wrap and microwave until fork-tender, about 15 minutes.
Meanwhile, spread the tofu on a large plate and press out the excess moisture with paper towels; set aside. Heat the olive oil in a large skillet over medium-high heat. Add the bell pepper and all but 2 tablespoons of the scallions; season with salt and pepper. Cook, stirring, until softened, about 5 minutes. Add the garlic, chili powder and cumin and stir to coat the vegetables. Add the tofu and 1/2 teaspoon salt and cook, breaking up any large chunks, until combined. Stir in the salsa. Remove from the heat.
Set the squash halves cut-side up on the prepared baking sheet (trim the bottoms so they sit flat, if necessary). Pat dry and season the insides generously with salt and pepper. Stir half of the cheese into the tofu mixture, then divide among the squash halves. Top with the remaining cheese and bake until the filling is hot and the cheese is melted, about 10 minutes. Top with the reserved scallions and assorted toppings.