Cut the zucchini into long noodles using a spiralizer (or use 1 pound store-bought zucchini noodles). Set aside.
Put a rimmed baking sheet in the oven and preheat to 425 degrees F. Toss the tomatoes with 1 tablespoon olive oil in a small bowl and season with salt and black pepper. Spread on the hot baking sheet and bake until the tomatoes are slightly softened and just browned around the edges, 7 to 10 minutes.
Meanwhile, cook the bacon in a medium nonstick skillet over medium heat until browned and crisp, about 7 minutes. Remove to a paper towel¿lined plate and wipe out the skillet. Melt the butter in the skillet and add the scallion whites and garlic; cook until softened, about 1 minute. Add the flour and stir to combine, about 30 seconds. Whisk in the milk, mustard, cayenne and 1/2 teaspoon salt. Cook, whisking, until slightly thickened, about 2 minutes. Remove from the heat and whisk in the cheese until smooth.
Heat the remaining 1 tablespoon olive oil in a large nonstick skillet over medium-high heat. Add the zucchini noodles and season with salt and black pepper. Cook, stirring, until the zucchini is just softened, 2 to 3 minutes. Using tongs, transfer the zucchini to the cheese sauce, leaving any extra liquid in the skillet. Cook over medium heat, gently tossing until coated; season with salt and black pepper. Top with the roasted tomatoes, bacon and scallion greens.