Preheat broiler to high (or oven to 500 degrees). Wash and dry all produce. Halve, peel, and dice onion. Peel carrot; quarter lengthwise, then cut crosswise into 1/4-inch-thick pieces. Dice potatoes into 1/2-inch cubes. Pat chicken dry with paper towels; season all over with salt, pepper, and half the Fry Seasoning.

Place potatoes in a medium bowl with enough salted water to cover by 2 inches. Bring to a boil and cook until potatoes are tender, about 15 minutes. Drain and return to pot. Mash with a potato masher or fork until smooth. Stir in 2 TBSP butter, salt, and pepper. (TIP: If potatoes are too thick, stir in a splash of water.)

Meanwhile, heat a drizzle of oil in a large pan over medium-high heat. Add chicken and cook, stirring, until browned and cooked through, 5-6 minutes. Transfer to a cutting board. If necessary, cut into bite-sized pieces. Place carrot in a medium bowl with a splash of water. Cover with plastic wrap. Microwave on high until soft, 3-4 minutes. Drain.

Heat a drizzle of oil in pan used for chicken over medium-high heat. Add onion and cook, stirring, until lightly browned and softened, 4-5 minutes. Stir in 1 TBSP butter until melted, then stir in flour and remaining Fry Seasoning. Cook for 1 minute. Gradually whisk in 1 cup water and stock concentrate. Reduce heat to medium and simmer until thickened, 2-3 minutes. Stir in peas, chicken, and carrot. Season with salt and pepper.

Transfer filling to an 8-by-8-inch baking dish (use a 9-by-13-inch baking dish for 4 servings). Evenly top with mashed potatoes. (TIP: It’s okay if the potatoes don’t reach the edge of the baking dish.) Evenly sprinkle with cheddar. Broil until cheese has melted, 2-3 minutes.

Transfer filling to an 8-by-8-inch baking dish (use a 9-by-13-inch baking dish for 4 servings). Evenly top with mashed potatoes. (TIP: It’s okay if the potatoes don’t reach the edge of the baking dish.) Evenly sprinkle with cheddar. Broil until cheese has melted, 2-3 minutes.