Finely grate the zest of the lime and divide between two bowls. Juice the lime into one bowl, add the sliced onion and a pinch of salt, and toss to coat. Set aside to pickle while you prepare the rest of the dish, tossing occasionally.
Add the feta, cilantro, olive oil and several grinds black pepper to the second bowl of zest. Smash with a fork until fully combined and spreadable.
Bring a pot of water to a boil, then reduce the heat so it's at a rapid simmer. Carefully lower the eggs into the water one at a time. Cook at least 6 ½ minutes (for a very jammy egg), or longer for a firmer yolk. Transfer to an ice bath and let sit for 2 minutes before peeling.
Toast your bread of choice in a toaster, skillet, or under the broiler. Add some of the smashed feta, then top with an egg and smash with a fork. Finish with the lime-pickled onions, more cilantro, a drizzle of oil, and flaky salt.
