Place the vinaigrette in a large saute pan and bring to a simmer on the grates of the grill. Add the figs and cook for 1 to 2 minutes.
Toss the mesclun greens in a large bowl with the olive oil and season with salt and pepper. Transfer to a large platter and using a slotted spoon, place the figs on top. Sprinkle the salad with the Stilton and drizzle with some of the Port Vinaigrette.
Heat grill to high. Heat oil in a medium saucepan on the grates of the grill. Add the onion and cook until soft. Add the Port and red wine and cook until thickened and reduced to 1/2 cup.
Transfer reduced wine mixture to a blender and add the molasses, balsamic vinegar, thyme and salt and pepper and blend until combined. With the motor running, slowly add the olive oil and walnut oil and blend until emulsified.