1.Preheat oven to 180°C.
2.Heat oil in a large frying pan over high heat; cook lamb, garlic and spices, stirring, for 5 minutes or until browned. Add tomatoes, beans and the water; bring to the boil. Reduce heat to medium-low; simmer, uncovered, for 10 minutes or until lamb mixture thickens, stirring occasionally.
3.Just before serving, spread corn chips over a large heatproof plate; top with lamb mixture, sprinkle with cheese. Bake nachos, uncovered, for 15 minutes or until heated through.
4.Make salsa fresca: combine ingredients in a medium bowl.
5.Combine avocado with half the salsa in a medium bowl; drop spoonfuls of the avocado mixture and sour cream over nachos. Top with remaining salsa.