How to Make It
In a small bowl, whisk vinegar and Dijon. Slowly whisk in 3 Tbsp. olive oil.
Melt butter with remaining 1 Tbsp. oil in a skillet over medium heat. Add mushrooms and cook, stirring, until they release their liquid, about 4 minutes. Add herbs and port; cook until wine evaporates, stirring occasionally.
Add artichokes and olives to skillet. Cook, stirring, until warm, 1 to 2 minutes. Remove pan from heat and season with salt and pepper.
In a large bowl, toss spinach with vinaigrette and divide among plates. Spoon artichoke mixture on top; sprinkle with tomatoes and cheese.