5 anchovy fillets, finely chopped
3 garlic cloves, pressed
1/2 cup extra-virgin olive oil
3 cups 3/4-inch cubes crustless country bread
1 cup (packed) coarsely grated Gruyère cheese (about 4 ounces), divided
Nonstick coconut oil spray
1 bunch mustard greens (about 12 ounces), center rib and stem cut from each leaf, leaves cut crosswise into 1/2-inch-wide strips
Preheat oven to 375°F.
Combine anchovies and garlic in small bowl. Gradually whisk in oil.
Place bread cubes in medium bowl.
Drizzle 2 tablespoons anchovy oil over, tossing to coat. Sprinkle bread with salt, pepper, and half of cheese; toss to coat.
Spray rimmed baking sheet with nonstick spray.
Scatter bread on sheet.
Bake croutons until crisp and golden, stirring occasionally, about 20 minutes. Set aside.
Measure 8 cups (loosely packed) mustard greens and place in large bowl (reserve any remaining greens for another use). Add croutons and remaining cheese to bowl.
Whisk 5 teaspoons lemon juice into remaining anchovy oil; season dressing with salt, pepper, and more lemon juice, if desired.
Add dressing to salad; toss to coat.