In a medium Dutch oven, add peas and water to cover by 1 inch. Bring to a boil over medium-high heat. Reduce heat to medium; cook, stirring occasionally, until peas are tender, 15 to 20 minutes. Drain and rinse under cold water until peas are cooled to room temperature; set aside.
In a medium bowl, whisk together vinegar, mustard, marmalade, salt, pepper, and garlic. Slowly whisk in oil in a steady stream. Add peas and onion to bowl, stirring to combine. Cover and refrigerate for at least 1 hour or up to overnight.
Arrange tomato slices on a serving platter. Spoon pea mixture over tomatoes. Sprinkle with chopped mint and Parmesan. Garnish with mint leaves and pepper, if desired.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/marinated-lady-peas-tomato-salad/