Wash the watercress thoroughly under cool running water, remove the coarse and tough stems, and dry the leaves completely. A salad spinner works well, followed by a brief air-dry on a clean towel.

Peel the tangerines, separate them into segments, and remove excess pith and any seeds. Thinly slice the red onion, then peel and cut the avocado into cubes or slices.

Whisk the fresh tangerine juice, blanco tequila, lime juice, honey, minced shallot, Dijon mustard, salt, and black pepper in a small bowl. Continue whisking until the honey is well incorporated.

Gradually whisk in the extra-virgin olive oil until the dressing is emulsified and lightly thickened. You may also place all dressing ingredients in a tightly covered jar and shake until combined.

Place the dry watercress, tangerine segments, and sliced red onion in a large bowl. Add the avocado and dressing just before serving, then toss gently to coat without breaking the avocado.