Combine potato, lentils, 1¼ cups water, and a pinch of salt in small saucepan. 

Bring to a boil, cover, reduce heat to low, and simmer until lentils are soft and potatoes are fork-tender, 14 to 16 minutes. 

Mash red lentil skordalia with back of fork until mostly smooth.

Stir remaining garlic, dill, vinegar, and 1 tbsp olive oil into red lentil skordalia. 

Season to taste with salt and pepper.