Whisk 2 cups cold water, 1 tablespoon vinegar, 1 teaspoon each sugar and salt, and pepper to taste in a bowl. Prick the pork a few times with a fork, then soak in the brine 15 minutes; remove and pat dry. Meanwhile, bring a saucepan of salted water to a boil. Add the green and wax beans and cook until crisp-tender, 4 minutes. Add the bell pepper and corn; cook 1 minute. Drain the vegetables, rinse under cold water and pat dry. Transfer to a bowl and add the kidney beans. Season the pork with salt and pepper. Heat 1 tablespoon olive oil in a nonstick skillet over medium-high heat. Add the pork and cook until golden, about 4 minutes per side; transfer to a plate. Wipe out the skillet; heat the remaining 1 tablespoon olive oil over medium heat. Add the shallot and cook 3 minutes. Add the remaining 2 tablespoons vinegar and cook until absorbed. Whisk in 1/2 cup water, half of the parsley, the mustard, the remaining 1/2 teaspoon sugar, and salt to taste. Simmer 3 minutes, then toss with the vegetables. Add the remaining parsley and season with salt and pepper.