Nutrition per serving may change if servings are adjusted.
½ of a medium red onion, cut into very thin wedges
⅓ cup red-wine vinegar
2 (12 ounce) pork tenderloins
½ teaspoon salt plus ⅛ teaspoon, divided
½ teaspoon ground pepper
1½ cups fresh blackberries, divided (see Tip)
1½ cups fresh raspberries, divided (see Tip)
¼ cup chopped fresh basil
2 tablespoons olive oil
9 cups fresh baby spinach
½ cup very thinly sliced celery (1 stalk)
4 ounces semisoft goat cheese, crumbled
Combine red onion and vinegar in a small bowl. Cover and let stand at room temperature 1 hour or chill up to 24 hours, stirring occasionally.
Trim fat from pork. Sprinkle the pork with ½ teaspoon of the salt and the pepper. For a charcoal grill, arrange hot coals around a drip pan. Test for medium-hot heat above the drip pan. Place the pork on grill rack over the drip pan. Cover and grill 25 to 30 minutes or until a thermometer inserted into the center of the pork registers 145°F. (For a gas grill, preheat grill. Reduce heat to medium-high. Adjust for indirect cooking. Place meat on grill rack over burner that is off. Grill as directed.) Transfer the pork to a cutting board. Cover with foil; let stand 3 minutes.
Meanwhile, place ½ cup of the blackberries and ½ cup of the raspberries in a blender or food processor. Cover and blend or process until smooth. Press the pureed berries through a fine-mesh sieve; discard seeds. Stir together the strained berries, basil, oil, and the remaining ⅛ teaspoon salt in a small bowl. Set aside.
To serve, divide spinach among six serving plates. Using a fork, remove the onion from the vinegar, allowing the excess vinegar to drip off; reserve the vinegar. Arrange the onion on the spinach on plates; top with celery. Thinly slice the pork crosswise; place on top of salads.
For dressing, stir the reserved vinegar into the pureed berry mixture. Drizzle dressing over the salads. Top the salads with the remaining fresh berries and the goat cheese.
Tip: If desired, substitute 3 cups fresh boysenberries for the blackberries and raspberries. Puree 1 cup of the boysenberries until smooth; press through a sieve and discard seeds. Top salads with the remaining 2 cups berries.