Preheat the oven to 300°F.
Tear or cut the loaf into small cubes. Slightly stale bread works best - it's easier to toast and blend. Spread the chunks out on a baking sheet in a single layer.
Season and toast. Drizzle olive oil over the bread chunks - just enough to coat lightly. Sprinkle on the garlic powder, onion powder, and parsley. Use your hands or a spatula to toss everything right on the pan until evenly coated. Place the pan in the oven and toast for 15-20 minutes, flipping halfway through. Keep a close eye during the last few minutes to prevent burning. The bread should be golden brown and crisp.
Cool and blend. Let the toasted bread cool completely before blending. Pulse in a food processor or blender until you reach your desired texture.
Store for later in an airtight container in the fridge for up to 1 week or in the freezer for up to 3 weeks.