Heat oven to 375° F. Toss cauliflower, oil, 1/4 tsp of the salt, 1/8 tsp of the garlic powder and the pepper in a large bowl. Spread onto a baking sheet; bake at 375° F for 25 minutes. Reduce heat to 350° F.
Bring a large pot of salted water to boiling.
Pulse bread in a chopper until crumbs are formed. Melt 1 tbsp of the butter in a small skillet. Add bread crumbs; cook over medium-high heat, 2 to 3 minutes.
Add pasta to boiling water. Cook 10 minutes. Drain and return to pot. Meanwhile, make sauce: Melt remaining 2 tbsp butter in saucepan over medium heat. Add flour and whisk for 2 minutes. Whisk in milk, remaining 1 tsp salt, the smoked paprika and remaining 1/8 tsp garlic powder and bring to a simmer. Cook 3 minutes, whisking occasionally. Remove from heat and whisk in Gouda.
Stir cauliflower and sauce into pasta. Spoon into a 13 x 9 x 2-inch dish. Top with bread crumbs. Bake at 350° F for 20 minutes.