Heat oil in a large Dutch oven over medium heat. Add onion; cook 5 minutes or until tender, stirring occasionally. Add garlic; cook 1 minute, stirring constantly. Add rice; cook 2 minutes, stirring frequently. Add water, 1 1/2 tablespoons dill, half of spinach, and half of mustard greens. Bring to a boil; cover, reduce heat, and simmer 20 minutes or until liquid is absorbed. Stir in remaining spinach, remaining mustard greens, 1 1/2 tablespoons dill, lemon juice, salt, and peppers; cook 30 seconds, stirring constantly.