Whisk 3 tablespoons reserved mandarin orange liquid, stir fry sauce, and orange juice concentrate together in a small bowl until sauce is smooth.
Heat 2 teaspoons vegetable oil in a large nonstick skillet over high heat until oil shimmers. Cook and stir 1/2 of the pork in hot oil until no longer pink in the center, about 3 minutes. Transfer cooked pork to a plate. Repeat with remaining vegetable oil and pork.
Place snap peas and sauce mixture in the same skillet, reduce heat to medium-high, cover the skillet with a lid, and cook until peas are tender yet still crisp to the bite, about 2 minutes. Stir pork and mandarin oranges into snap pea mixture; cook and stir until heated through, about 1 minute.