Preheat the broiler to high.
In a small bowl, whisk together the mustard and red wine vinegar, and slowly add the olive oil in a steady stream, whisking until combined. Season with salt and pepper.
In a large bowl toss together the lettuces, radishes, and apples.
Arrange 8 baguette slices on a baking sheet and drizzle with olive oil. Broil for about 30 seconds or until beginning to brown. Remove from the oven, flip over and top with goat cheese slices. Drizzle with olive oil and broil for another minute or so until bubbling and browned. (Stand right by the oven – it can quickly burn if you don’t watch it!)
Toss the salad mixture with the vinaigrette, and season with additional salt and pepper. Divide among four plates and top with the warm goat cheese crostini. Serve immediately.
NOTE: You can make more of a composed salad if you like, arranging the radishes on the bottom of the plate, drizzling with vinaigrette, and then adding the remaining salad (mixed with radishes and apples) on top and goat cheese on top. It’s a really pretty salad, so I like to arrange each plate.