Stir together bread crumbs, onion, lemon-pepper seasoning, Cajun seasoning, Italian seasoning, paprika, and garlic salt in a small bowl.
Clean cauliflower and broccoli and cut into florets. Cut broccoli stems into thick slices. Place each vegetable into its own 1-gallon, resealable plastic bag. Pour 1 tablespoon olive oil into each bag and 1/2 of the bread crumb mixture. Seal the bags and shake well to ensure vegetables are thoroughly and evenly coated. Set aside for at least 10 minutes or refrigerate until ready to use.
Preheat the oven to 350 degrees F (175 degrees C). Spray a baking pan with cooking spray.
Place vegetables on the prepared pan.
Roast in the preheated oven until crisp tender, about 20 minutes.