Sauté the aromatics. Heat olive oil in a large pot over medium heat. Add diced onion and cook for 5-6 minutes until translucent. Add minced garlic and cook for another 30 seconds until fragrant.
Add the spices. Stir in smoked paprika, cumin, and cayenne pepper. Cook for 1 minute to toast the spices and release their flavors.
Incorporate the liquids and pumpkin. Add vegetable broth, pumpkin puree, and fire-roasted tomatoes. Stir well to combine all ingredients.
Simmer the soup. Bring to a gentle boil, then reduce heat and simmer uncovered for 20 minutes, allowing flavors to meld together.
Blend until smooth. Remove from heat and use an immersion blender to puree until completely smooth. Alternatively, transfer in batches to a regular blender (be careful with hot liquid!).
Finish with cream. Return to low heat and stir in heavy cream. Season with salt and pepper to taste. Add maple syrup if desired for balance. Keep warm on low heat.
Make grilled cheese croutons. Butter one side of each bread slice. Place two slices butter-side down in a skillet over medium heat. Top with shredded cheese and remaining bread slices (butter-side up). Cook until golden brown on both sides, flipping once.
Cut into croutons. Transfer grilled cheese sandwiches to a cutting board and let cool slightly. Cut into 1-inch cubes.
Serve immediately. Ladle the hot bisque into bowls. Top each serving with several grilled cheese croutons and a sprinkle of smoked paprika if desired.