Spinach Salad with Blue Cheese with seasoning

1 tablespoon lemon juice (or to taste) 3/4 teaspoon Dijon mustard 3 tablespoons olive oil 1/2 lb cleaned baby spinach 1 cup thinly sliced mushroom 4 slices[...]

1 (6 ounce) bag baby spinach, washed and dried (if leaves are too big, chop them coarsely) 1/3 cup crumbled feta cheese or 1/3 cup any other white cheese,[...]

1/4 cup white vinegar 2 teaspoons Dijon mustard 1 garlic clove , minced 1/2 teaspoon ground pepper 2/3 cup olive oil 4 ounces crumbled blue cheese 10 ounces[...]