Heat the butter in a large frying pan and gently fry the onion for 5 minutes. Add the garlic, red pepper and cumin and cook for a few minutes. Add the chopped tomatoes, chard stems, balsamic vinegar and 250ml water, stir and bring to a simmer. Pop the lid on and let everything cook down for 10 minutes to make a chunky sauce. Stir in the chard leaves and cover the pan for 5 minutes to allow them to wilt. Take the lid off, season to taste and, if needed, leave to reduce again with the lid off for a few minutes for the sauce to thicken.
Push the vegetables aside using a spatula to make a small gap in the sauce and crack an egg in. Repeat for the other three eggs. If you pop the lid back on the eggs should be ready (whites set, and yolk runny) in about 3-4 minutes. Scatter over some fresh herbs, a dollop of yoghurt or feta and finish with sprinkling of cayenne pepper or paprika and a squeeze of lemon juice.