Preheat oven to 400°F.

Scrub potatoes well. Do not peel. Prick each potato several times with a fork. Place potatoes directly on oven rack positioned in center of oven. Bake until fork easily inserts into center of potato, approximately 1 hour.

With a sharp knife, cut each baked potato in half, lengthwise. Scoop out flesh of potatoes leaving about a ¼“ rim around the edges and bottom of each potato half to allow the potato shell to hold its shape. Place hollowed out potato halves on parchment- or tinfoil-lined rimmed baking sheet.

Mash potato flesh well or press through a potato ricer into a medium-sized bowl. Add tuna, egg, sour cream, butter, Parmesan cheese, mustard, onion salt/powder, garlic salt, celery salt, and pepper. Mix well to ensure all ingredients are incorporated.

Lightly brush inside and rim edges of each potato shell with olive oil. Spoon potato-tuna mixture into shells, generously stuffing each, and mounding tops. Sprinkle tops of potatoes with the cheddar cheese. Bake at 400°F for 10-12 minutes. Garnish with sliced green onions, pea shoots, and/or microgreens at time of serving, if desired. Serve hot.

To make ahead and freeze: Store unbaked stuffed potatoes (minus the cheddar cheese topping) in airtight freezer container. Bake from frozen state, at 400°F, for approximately 30 minutes then add the shredded cheese topping and continue baking potatoes for about 8-10 minutes longer or until cheese is melted and potatoes are heated through.