For this salad, look for Fuyu persimmons, which also may be labeled "ready to eat." They can be eaten while they are still firm, unlike the larger Hachiya persimmons, which can only be eaten when very soft.
Combine the lemon juice, shallots, mustard, and marjoram in a medium bowl, and whisk to combine. Slowly add olive oil, whisking constantly, until incorporated. Season with salt and pepper.
Toss escarole with just enough vinaigrette to coat. Arrange persimmon slices over greens, and sprinkle with pomegranate seeds, if using. Serve remainingvinaigrette on the side.