Bring 1 inch of water to a boil in a 3qt saucepan over high heat. Add your eggs in and cover, letting cook for 10 minutes. Prep a large bowl full of water and ice, leaving some space to add in the eggs to cool after they cook.
While your eggs are cooking, place your sliced cucumbers in a fine mesh strainer set over a bowl and season them with salt. Toss everything around and let sit for later.
Once eggs are done cooking, add them to your bowl with ice water and let them cool for a minute. Remove them one by one, peeling them as you go.
In a large mixing bowl, roughly mix together your eggs, Greek yogurt, Feta cheese, marinated cucumbers, dill, garlic, olive oil and lemon juice. Season to taste with salt and pepper. Note: You can use a large serving fork to mash everything up. Add more avocado along with an extra drizzle of olive oil if needed. You can make this egg salad very chunky or more on the smoother side depending on how well you smash and mix everything together.
To assemble sandwiches: Layer a generous stack of cucumber slices on one slice of bread and season with salt. Top with a generous portion of egg salad along with an extra squeeze of lemon juice an a sprinkle of salt. Close the sandwich with another slice of bread, cut in half diagonally and enjoy! Note: When cutting, use a sharp bread knife and cut gently and in a sawing motion to help keep the sandwich intact. Alternatively, you can wrap the sandwich in parchment paper or cling wrap and then cut it.