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.