Place eggs in a medium saucepan with water to cover. Bring to a rolling boil over high heat, cover, and simmer 5 minutes. Remove from heat, and let eggs sit in pot with water for 5 minutes. Cool eggs in a large bowl of ice water for a minute or so. Peel shells, and tear eggs into large pieces. In a bowl, gently mix together eggs, mayonnaise, olive oil, garlic, salt, and pepper. Place watercress on 1 slice whole wheat bread, layer with egg salad, and top with chives and radishes. Cover with second slice bread and serve.