Preheat the oven to 400ºF. Place 1 lb seedless (any color) grapes on their stems, cut into 4 equal clusters on a sheet pan and coat lightly with the oil. Roast for 5 minutes.
Prepare salmon: Season 4 (6 oz) salmon fillets with kosher salt and freshly ground black pepper. Mix 2 tsp Dijon mustard and 2 tsp mayonnaise together in a small bowl. Spread evenly over the top (flesh side) of each fillet. Spread ¼ c pecans or walnuts, finely chopped on a small plate. Press the mustard coated side in the nuts to coat evenly. Transfer to a plate.
When the grapes have cooked for 5 minutes, remove the pan from the oven. Add the fillets, skin side down, to the sheet. Return to oven and continue cooking until grapes are slightly shriveled and the salmon is barely opaque when prodded in the center, about 15 minutes.
Meanwhile make the sauce: Melt 1 tbsp of butter in a small saucepan over medium heat. Add 1 tbsp shallot, minced and cook, stirring occasionally, until softened but not browned, about 1 to 2 minutes. Stir in 1 c dry red wine, such as Pinot Noir or Shiraz, 1 tsp balsamic vinegar, 1 tsp honey or light brown sugar, ½ tsp Dijon mustard and ¼ tsp fresh thyme, coarsely chopped and bring to a boil over high heat. Cook, stirring occasionally, until the mixture has reduced to about 3 tbsp, about, 5 to 7 minutes. Remove from the heat. Cut 1 tbsp butter into cubes. Add to saucepan and whisk until the butter melts into the sauce. Season to taste with salt and pepper. Set the sauce aside (it will stay warm, do not reheat).