Heat oil in a Dutch oven over medium-high heat. Add mustard seeds and next 5 ingredients (mustard seeds through garlic); sauté 1 minute (mustard seeds will pop). Stir in green beans and potato; cook 5 minutes, stirring occasionally. Add water and lemon juice; cover, reduce heat to low, and cook 10 minutes or until potato is tender. Garnish with lemon rind, if desired.