To toast the pine nuts, an easy way to do so is on the stovetop. Heat the nuts in a nonstick pan while stirring constantly, so they don't burn, until golden brown on all sides.
To prepare the vinaigrette, in a small bowl, whisk together the olive oil, vinegar, basil, garlic, and sugar until the sugar is dissolved.
Gently mix in the fresh basil.
Season with salt and pepper.
In a large bowl, combine the spinach, red onion and pine nuts.
Gently toss the avocado in some of the vinaigrette.
Dress the salad with enough of the vinaigrette to just coat the leaves.
Adjust the seasonings.
Portion the salad on plates and garnish with the avocado slices.