Spread cream cheese mixture over tortillas. Top with spinach, smoked salmon, cucumber, and onion. Drizzle with remaining 1/4 cup dressing. Tightly roll up tortillas, tucking in ends (use a toothpick to secure, if needed). Serve immediately (or wrap in plastic wrap and chill up to 24 hours). Combine 1 cup mayonnaise and/or plain Greek yogurt, 3/4 cup sour cream, 1/2 cup lightly packed fresh parsley, 1/2 cup lightly packed fresh tarragon, 1/3 cup lightly packed fresh chives, 2 tablespoon fresh lemon juice and/or white wine vinegar, 1 anchovy fillet (or 1/2 teaspoon Anchovy paste), 1 teaspoon minced fresh garlic, 1/4 teaspoon salt, 1/8 teaspoon black pepper, and a pinch of cayenne pepper in a blender or food processor; process until nearly smooth, with flecks of herbs. If you like, blend in an additional 1 tablespoon lemon juice. (To store, transfer to a jar or airtight container. Chill, covered, up to 5 days.)
