2 medium navel oranges
1 small clove garlic, finely chopped
2 tablespoons sherry vinegar
1 teaspoon Dijon mustard
Pinch of salt
1/4 cup extra-virgin olive oil
1/2 medium red onion, thinly sliced
2 medium avocados, sliced
1 head Romaine lettuce, chopped and washed
Segment the oranges over a small bowl (see how here). Squeeze any remaining juice from the peels and membranes into the bowl.
Strain the orange segments, reserving the juice. In a small bowl, combine one tablespoon of the orange juice with the garlic, vinegar, mustard, and salt. While whisking, pour the olive oil into the bowl in a thin stream, and continue whisking until all the oil has been added and the dressing is smooth and emulsified. (Save or drink the remaining unused orange juice.)
Combine the lettuce, strained orange segments, onion, and avocado in a large salad bowl. Drizzle the dressing over the salad and toss to combine. Serve immediately.