Preheat the oven to 180C/360F/Gas 4.
Brush the bread slices with the garlic and a little olive oil, and bake in the oven until golden and crisp (about 10 minutes). Remove from the oven and allow to cool.
Meanwhile, make the avocado mixture. Mash the avocado with the goats' cheese.
Fold in two tablespoons of olive oil, the lemon juice, basil and onion. Season to taste.
Top each crostini with a mound of the avocado mixture, and serve.
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