Pound garlic and chilies to a rough paste in a mortar.
Add dried shrimp and pound lightly.
Add beans and pound gently to bruise, not crush.
Add tomatoes, pound gently.
Season with lime juice, fish sauce, and erythritol.
Add jicama and toss using the pestle and a spoon.
Taste — it should be sour, spicy, salty, with a hint of sweetness.
Serve topped with crushed nuts.