Place onions in a medium bowl, season with 1/4 teaspoon Kosher salt, set aside while you prep the remaining ingredients.
Add the hearts of palm and tomato to the onions, add fresh 2 tablespoons fresh lemon juice, drizzle with 2 tablespoons extra virgin olive oil, 1/4 teaspoon salt and fresh black pepper.
Place arugula in a large salad bowl, and arrange the avocado.
Pour everything over the salad and serve right away, toss before serving.