From the quantities listed I would say that's a hearty meal for one adult, a reasonable meal for one adult and one child, and if you serve it with an extra helping of veg, for instance broccoli, you could fill up your hypothetical child and adult or possibly stretch it to 2 adults.
The bulk is 200 g of lentils and peas plus small onion etc. The topping is one sweet potato. If I'm making a veggie sheps pie I'd be doubling those quantities for me and dh but I'd possibly expect to have some leftovers. Which might not happen. One sweet pot doesn't make much mash for a topping.