In a small bowl, combine the mayonnaise and Dijon mustard until smooth. Halve the avocado, remove the pit, scoop out half and slice thinly. Lightly season the avocado slices with 1/8 tsp salt and a pinch of black pepper. Slice the tomato into 3 even slices and pat dry to avoid sogginess.

Assemble sandwich

Spread the mayonnaise-mustard mixture evenly on one side of each sourdough slice. On one slice (the bottom), layer the avocado slices in a single layer, then arrange the turkey slices evenly on top of the avocado. Add the Swiss cheese slice over the turkey, then place the tomato slices and red leaf lettuce. If using pickles or hot sauce, add them now. Close the sandwich with the top slice of sourdough, spread side down.

Grill sandwich (optional but recommended)

Heat a skillet or griddle over medium heat. Add 1 tsp unsalted butter and let it melt and foam. Place the sandwich in the skillet and press gently with a spatula. Cook 2–3 minutes until the bottom is golden brown. Flip the sandwich, add remaining butter to the pan edge or spread on the other slice beforehand, and cook another 2–3 minutes until the bread is golden and the cheese has softened. Remove from heat and let rest 1 minute before cutting in half on the diagonal.

Side: Mixed Green Salad

Combine the mixed salad greens, cucumber slices, halved cherry tomatoes, and thinly sliced red onion in a medium bowl.

In a small jar or bowl, whisk together the extra-virgin olive oil, red wine vinegar, honey, 1/8 tsp salt, and a pinch of black pepper until emulsified.

Drizzle the dressing over the salad just before serving and toss gently to coat evenly. Taste and adjust seasoning if needed.

Finishing & Serving

Place the grilled sandwich on a plate alongside the mixed green salad. Serve immediately while sandwich is warm. Estimated accompaniments: a pickle spear or kettle chips if desired.