Add chopped onion and sauté until soft and slightly translucent with a mild sweet aroma

Stir in cauliflower and bell pepper, cooking until tender with light golden edges

Sprinkle in marjoram, salt, and black pepper, stirring to evenly coat the vegetables

Cook until the mixture becomes fragrant and slightly caramelized

Remove from heat and mix in pesto until everything is well coated and glossy

Arrange toasted bread slices on a baking sheet in a single layer

Spoon the warm vegetable mixture evenly over each slice

Top generously with shredded cheddar cheese, covering the surface

Place under a preheated broiler and cook until the cheese melts and forms golden spots

Remove carefully once the tops are bubbly and lightly browned

Serve immediately while hot and melty