Isn't iron in spinach insanely difficult for humans to actually absorb? Quick googling says it's around ~2% of total iron in spinach which we can absorb, so instead of eating 100g to get 2.7g you'd need to eat 5kg of spinach per day.

That might be the recommendation for a very small woman.

For men of average size, the recommended daily intake of iron varies between countries, but it can be as large as 14 mg, which would need at least 400 g of cooked lentils per day, according to your list, which corresponds to lentils cooked with an unknown amount of water, so it is difficult to compare it with lentils cooked in different ways, though it seems that these 100 g of cooked lentils correspond to about 40 g of raw lentils with about 60 g of water.

100g is a large volume of loose spinach and dry lentils. That's a hearty entree for a hungry lass once cooked.