
Roast the squash. Preheat the oven to 425°F. Place the diced butternut squash on a sheet pan and toss with 2½ tablespoons olive oil, 1 teaspoon kosher salt, ½ teaspoon black pepper, and the red pepper flakes.
Spread into an even layer and roast for 25–35 minutes, until very tender and lightly browned on the edges. Toss once with a spatula halfway through. Set aside.
Caramelize the onions. While the squash roasts, heat the butter and 2 tablespoons olive oil in a 10-inch sauté pan over medium heat. Add the onions and cook for 12–15 minutes, stirring occasionally, until golden brown.
Stir in the apple cider vinegar and agave nectar. Simmer for 4–6 minutes, until the liquid reduces slightly.
Combine the mixture. Add the roasted squash to the pan with the onions. Lightly mash with a fork so the squash blends in but still has some texture. If the mixture feels dry, stir in a few tablespoons of apple cider or apple juice. Taste and adjust seasoning as needed. Keep warm over low heat.
Assemble the bruschetta. Spread a generous layer of queso fresco or ricotta on each slice of toasted bread. Spoon the warm squash and onion mixture over the top. Sprinkle with pepitas, a pinch of salt and serve right away.