1 ½ tablespoons olive oil, divided, or more as needed
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2 cups chopped fresh spinach
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½ cup giardiniera, drained
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2 slices mozzarella cheese
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2 slices provolone cheese
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2 slices Asiago cheese
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2 slices Fontina cheese
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3 slices Roma tomato, cut lengthwise, or more to taste
Instructions
Mix butter and garlic in a small bowl until well combined. Spread 1/2 of the butter onto one side of each slice of bread; set aside.
Heat 1 tablespoon oil in a large skillet over medium-low heat; stir in spinach and giardiniera. Saute until spinach is wilted and mixture is heated through, 3 to 5 minutes. Remove to a bowl and wipe out the skillet.
Place 1 slice of bread, buttered-side down, into one side of the warm skillet. Heat 1/2 tablespoon oil in the other side of the skillet. Place mozzarella slices in the skillet and cook until soft, 1 to 2 minutes. Place mozzarella slices on top of the bread in the skillet. Repeat with the provolone, Asiago, and Fontina slices.
Add spinach mixture and tomato slices to the skillet, adding more oil if necessary, and cook until warm, 2 to 3 minutes. Place spinach mixture on top of the cheese, followed by the tomatoes and the remaining slice of bread, buttered-side up. Flip the sandwich and cook until browned and cheese has melted, 5 to 10 minutes.