Make the Dressing: In a small bowl whisk together 1 egg yolk, 1 grated clove of garlic and 1 teaspoon of dijon mustard. Combine it with ⅓ cup of sherry vinegar. Make an emulsified vinaigrette by slowly drizzling in ⅓ cup each of avocado oil and extra virgin olive oil. The dressing should appear creamy and coat the back of a spoon without separating. Season with sea salt and freshly cracked black pepper to taste.
Prepare the Salad: Lightly coat your clean grill grates with a small amount of avocado oil, about a teaspoon. I put it on a paper towel then rub the top of the grates with the oiled rag. Preheat a charcoal grill to 500˚.
Place the 4 eggs in a pot and cover with cold water. Bring to a boil, turn off the heat and cover with a lid. Allow the eggs to cook in the water for 8 minutes, then drain the hot water and cover with ice water. Peel the eggs.
Prepare the vegetables and tuna steaks for grilling by snapping off the woody ends of 1 bunch of asparagus and cutting 1 pound of new potatoes in quarters or halves (depending on size) and 1 red onion into 1 inch thick chunks. Grill the vegetables until tender, rotating on all sides until slightly charred, about 2 minutes for the asparagus, and 10 minutes for the potatoes and onion. Season with salt and pepper and grill the 4 tuna steaks to medium rare, cooking on both sides for about 2 minutes a side.
Remove from the grill and place the veggies in a bowl, season with sea salt and black pepper to taste, and allow to cool for 10 minutes. Once cool, toss with ½ a cup of the salad dressing to marinate.
Assemble the Salad: Place 3 ounces of baby spinach on a platter, and garnish with the grilled tuna, asparagus, red onions and potatoes, as well as the 4 eggs, 1 cup crumbled feta and ⅓ cup pitted kalamata olives. Drizzle more salad dressing on top, or serve on the side if the salad will be sitting for more than 5 minutes.