Peel, then cut potatoes into 1-inch pieces. Add potatoes, 1 tsp salt and enough water to cover (by approx. 1 inch) to a large pot (use same for 4 ppl). Cover and bring to a boil over high heat. Once boiling, reduce heat to medium. Simmer uncovered, until potatoes are fork-tender, 10-12 min.
Meanwhile, strip 1 tbsp (2 tbsp) thyme leaves from stems, then finely chop. Roughly chop parsley. Peel, then mince or grate garlic.
Heat a large oven-proof pan over medium heat. When hot, add ½ tbsp (1 tbsp) oil, then Beyond Meat®. Cook, breaking up Beyond Meat® into smaller pieces, until golden-brown, 4-5 min.** Carefully drain and discard excess fat. Add 1 tbsp (2 tbsp) butter, then mirepoix, thyme and garlic. Cook, stirring often, until veggies soften slightly, 3-4 min. Season with salt and pepper.
Add tomato sauce base, then sprinkle flour over top. Cook, stirring often, until Beyond Meat®and veggies are coated, 1-2 min. Add peas, soy sauce, broth concentrate and ¾ cup (1 ½ cups) water. Bring to a boil over high.Once boiling, reduce heat to medium. Cook, stirring often, until sauce thickens slightly and veggies are tender, 3-4 min. Season with salt and pepper, to taste. (NOTE: If you don't have an oven-proof pan, transfer Beyond Meat® filling to a 8x8-inch baking dish for 2 ppl or a 9x13-inch dish for 4 ppl.)
When potatoes are fork-tender, drain and return them to the same pot, off heat. Mash cheese, half the parsley, ¼ cup (½ cup) milk and 2 tbsp (4 tbsp) butter into potatoes until creamy. Season with salt and pepper, to taste.
When Beyond Meat® filling is done, top with mashed potatoes, spreading into an even layer. Broil in the middle of the oven until potato topping begins to brown, 4-5 min. Remove cottage pie from the oven and let stand for 5 min. Divide cottage pie between plates. Sprinkle remaining parsley over top.
If you've opted to get Beyond Meat®, add ½ tbsp (1 tbsp) oil to the pan, then patties. Cook and plate it the same way as the beef, until golden-brown.**