This dish is a fast take on the usual long-simmered greens. Swap out other hearty greens like kale, collards, or turnip greens for the mustard greens if you prefer.
Heat oil in a Dutch oven over medium. Add garlic; cook, stirring often, until garlic is golden brown and crispy, about 1 minute. Stir in greens, in batches; cook until wilted, 1 to 2 minutes, before adding more greens. Cover and cook, stirring occasionally, until tender-crisp, 10 to 12 minutes. Stir in lemon juice and 1/4 teaspoon crushed red pepper. Sprinkle with salt and pepper. Stir in an additional 1/4 teaspoon crushed red pepper, if desired.