1. Preheat oven to 350°F with rack in middle.
2. Cover potatoes with water in a small pot and season well with salt, then simmer until tender, about 15 minutes.
3. While potatoes cook, toast almonds and bread crumbs separately in oven until pale golden, 8 to 10 minutes, then cool.
4. With motor running, drop garlic into a food processor and chop. Add nuts and bread crumbs and finely grind. Pulse in water, 3/4 teaspoon salt, and 1 tablespoon lemon juice.
5. Drain potatoes and coarsely mash with fork, then add to processor with oil and pulse to combine. Add lemon juice to taste and thin with a little water if desired.