Preheat the oven to 425°F. Cover a rimmed baking sheet with parchment paper or aluminum foil.
Arrange the cubed butternut squash and chopped red bell pepper on the prepared baking sheet. Spread the vegetables into a single, even layer to encourage uniform roasting.
Lightly coat the vegetables with olive oil spray. Season with salt, freshly ground black pepper, and rosemary, then toss thoroughly until the seasonings are evenly distributed.
Roast for 25 to 30 minutes, or until the squash is tender when pierced with a fork. Larger cubes may require additional cooking time.
While the vegetables roast, pour the balsamic vinegar into a small saucepan. Bring it to a gentle simmer over medium to medium-high heat, then cook until the liquid has reduced by slightly more than half.
Remove the balsamic reduction from the heat once it coats the back of a spoon and measures approximately 2 to 3 tablespoons. Allow it to cool briefly; it will continue to thicken as its temperature decreases.
When the vegetables have finished roasting, remove the baking sheet from the oven. Immediately dust the hot squash and pepper lightly with garlic powder, then stir to distribute the seasoning.
Prepare the eggs by frying, poaching, or soft-boiling them. For runny yolks, cook only until the whites are set; eggs fried over medium-low heat work especially well.
Divide the roasted vegetables evenly among four plates, using approximately one-quarter of the mixture for each serving. Place two cooked eggs over each portion.
Finish each plate with 1 to 2 teaspoons of the balsamic reduction and serve promptly.