Peel and halve the red onion; using a sharp knife or mandoline, slice very thin rings. Core the tomato and slice into 8 thin rounds. Lay both on paper towel to absorb excess moisture for a few minutes.

Assemble greens

Place mixed garden greens in a medium bowl and toss lightly with 2 teaspoons of the prepared sherry vinaigrette to coat (reserve remaining vinaigrette for plating).

Layer bagel

Spread about 2 tablespoons of the garlic & herb spread evenly on each toasted bagel half. Top each bottom half with a small handful (about 1 cup) of dressed garden greens, 3 oz (about 3 slices) smoked salmon, 2–3 tomato slices, a few red onion rings, and 3/4 tablespoon capers. Finish with the top half of the bagel or serve open-faced.

Garlic & Herb Spread

In a medium bowl, combine softened cream cheese, sour cream, and mayonnaise. Add the minced garlic, snipped chives, chopped dill, lemon zest, lemon juice, salt, and black pepper. Use a fork or small whisk to blend until smooth and spreadable, stopping when evenly combined. Taste and adjust salt or lemon as needed. Cover and chill until ready to use (can be made up to 24 hours ahead).

Sherry Vinaigrette

Whisk sherry vinegar, Dijon mustard, honey, minced shallot, salt, and black pepper in a small bowl. While whisking, slowly drizzle in the olive oil until emulsified. Alternatively, combine all ingredients in a jar, seal, and shake vigorously. Taste and adjust seasoning. Keep refrigerated if not using immediately; bring to room temperature before tossing with greens.