1. Position rack in upper third of oven; preheat broiler. Line a small baking sheet with foil.
2. Cook pasta according to package directions. Drain, reserving ½ cup of the cooking water.
3. Meanwhile combine dill and panko in a small bowl. Divide goat cheese into 4 portions; shape each into a 1-inch wide disk. Coat the disks in the panko, lightly patting the mixture onto the cheese to help it stick. Place on the prepared baking sheet and lightly coat the tops with cooking spray. Set aside.
4. Heat oil in a large skillet over medium heat. Add onions and cook, stirring, until lightly browned, 5-6 minutes. Add tomatoes, garlic, salt and pepper; cook until the tomatoes release their juice, 1 to 2 minutes. Stir in the reserved ½ cup water, scraping up any browned bits. Stir in spinach and the pasta; remove from heat.
5. Broil the goat cheese rounds, watching closely, until light brown and crispy on top, 1 to 2 minutes. Serve each portion of pasta topped with a goat cheese medallion.