Preheat oven to 425 degrees F (220 degrees C).
Line a large baking sheet with parchment paper. Add Red Bell Pepper (3), Sweet Potato (2), Yellow Onion (1), Garlic (4 clove) and Tomato (2) to the baking sheet, drizzle them with the Olive Oil (1/3 cup) and sprinkle them with Salt (1/2 teaspoon).
Roast vegetables on the center rack of the oven for 35 minutes, until they are soft and beginning to brown.
Heat the Vegetable Broth (3 cup) on the stove or in the microwave.
Carefully add the vegetables to a high speed blender along with the hot vegetable broth. Blend until the contents are perfectly smooth.
Heat a large pan or griddle over medium heat.
Gather Bread (8 slice), Cheese (4 slice) and Butter (4 tablespoon). Add a slice of cheese between two slices of bread, and spread butter on the outside of each slice. Repeat until you have 4 sandwiches.
Grill the sandwiches until golden and crisp on one side, about 2-3 minutes.
Flip the sandwiches and grill for another 2-3 minutes.
Serve the soup into 4 bowls. Cut grilled cheese sandwiches into small squares, and top off each bowl of soup with croutons.