Preheat oven to 400°F; lightly grease a 9x13-inch dish with 1 tablespoon oil.
Toss cauliflower and broccoli with 1 tablespoon oil, salt, and pepper; spread on baking sheet and roast 15 minutes until slightly tender.
Meanwhile, drain cashews; blend with milk, yeast, garlic, onion powder, salt, and pepper until completely smooth and creamy.
Transfer vegetables to dish; pour sauce evenly over and stir gently to coat.
Sprinkle with panko; bake at 375°F for 20 minutes until golden brown and bubbly.
Remove; rest 5 minutes, garnish with parsley, and serve warm.