In a large pot, bring water to boil, add the broccoli florets and boil for 2 minutes. Drain the broccoli in a colander and rinse with cold water to stop the cooking process.
Place the broccoli in a medium casserole dish; set aside.
Heat a medium saucepan on medium-high, melt the butter, then add the flour and cook, stirring, until it turns to light golden. Gradually pour in the milk while whisking.
Add garlic powder, onion powder, oregano, salt, and pepper. Continue cooking about 2 minutes, stirring occasionally, until sauce is thickened and bubbly.
Remove from the heat and add the cheddar cheese; stir until completely melted.
Pour the sauce evenly over the broccoli.
Heat a medium skillet over medium-high heat, add the olive oil and onion. Cook onion, stirring occasionally until golden.
Sprinkle the onion evenly on top of the broccoli casserole. Top with crumbled croutons and bake about 30 minutes until golden brown and bubbly.
Remove from the oven. Serve hot and enjoy!