Using a food processor, blitz celery, carrots, onion, garlic, and parsley and process until everything is uniform and processed to little bits. You'll need to scrape down the sides and process to make sure everything is even. EDIT: Upon further testing, I find that the filling can be a little too wet if you use a food processor. I recommend chopping everything very fine with your knife by hand!

In a large bowl, combine the processed veggie mixture with ground round, fish sauce, salt, ground pepper, flax meal. Stir until everything is incorporated and let sit for about 5 minutes for the flax meal to rehydrate in the mixture (this will act as the binder).

Prepare the spring roll wrappers by peeling them apart on a plate. If you can roll fast, you don't need to cover, but I highly recommend covering with a clean, damp tea towel to keep the wrappers from drying out.

Give the filling mixture a good mix to ensure everything is incorporated. To roll the lumpia, turn the spring roll wrapper so a corner points towards you. Add about 1 tbsp of filling per wrapper in the bottom third of the wrapper, then use one corner to tuck the filling and roll up 1/3 of the way. Tuck the left and right corners over the filling, then finish the roll, using some water to seal the edge. Arrange on a plate in a single layer with parchment paper in between. Freeze first to ensure the lumpia stays together while frying, but you can simply freeze while you heat up the oil.

Heat up 2 inches of oil in a deep pot to 400F (medium high heat). Fry the lumpia for about 3-5 min, until golden and crispy. Be sure to flip them in the oil so it's cooked evenly and doesn't stick to each other.

Once golden, let drain on a paper towel or tea towel.

Serve with plum sauce or sweet chili Thai sauce!