Directions:

1. Preheat oven to 450°F. Toss 2½ cups cauliflower and 1½ teaspoons oil together on a large rimmed baking sheet; spread in an even layer. Roast until browned, 15 to 20 minutes. Let cool for 5 minutes. Finely chop the cauliflower; transfer to a medium bowl.
2. Meanwhile, heat 1 tablespoon oil in a large nonstick skillet over medium-high heat. Add ¼ cup shallots; cook, stirring often, until softened, about 1 minute. Add 8 cups spinach in batches; cook, stirring often, until wilted, 3 to 4 minutes. Stir in ¼ cup dill, chopped garlic and ½ teaspoon pepper; cook, stirring often, until fragrant, about 1 minute. Transfer the spinach mixture to a fine-mesh strainer placed over a large bowl; let cool slightly, about 5 minutes. Wipe the skillet clean. Gently press the spinach to remove excess liquid, patting dry with paper towels if needed. Discard the liquid. Add ¾ cup feta, the spinach mixture and ¼ teaspoon salt to the cauliflower; stir to combine.
3. Spread 2 tablespoons fontina on each of 4 bread slices; top with about ½ cup cauliflower mixture, 2 tablespoons fontina and the remaining bread slices. Heat 1 teaspoon oil in the skillet over medium heat. Cook 2 sandwiches (place another skillet on top of sandwiches to weigh them down) until golden brown on the bottom, about 2 minutes. Add ½ teaspoon oil to the pan, flip the sandwiches and cook until golden brown on the other side and the cheese is melted, about 2 minutes more. Adjust heat as needed to prevent the bread from burning. Repeat the process with the remaining 1½ teaspoons oil and 2 sandwiches.