Bring a medium pot of water to a boil with a large pinch of salt. Peel the sweet potato, then dice into 1/2-inch pieces. Once boiling, add the sweet potato to the pot and cook for about 12 minutes, until fork-tender.

Meanwhile, halve, peel, and finely dice the red onion. Finely dice the celery. Halve the lemon. Heat 1 tablespoon olive oil in a large pan over medium heat. Add the onion and celery and cook, tossing, for 5 minutes, until softened. Season with salt and pepper, then transfer to a medium bowl to cool.

When the sweet potatoes are tender, remove from the pot with a slotted spoon and set aside with the onions and celery. Reduce heat to a low simmer, then add the salmon to the water and cook until flakey and opaque, 7-8 minutes. Remove from water and set aside to cool.

With a fork or potato masher, thoroughly mash the sweet potato. Then, mix in the onion, celery, thyme, panko, and Old Bay (to taste). Using a fork, flake the salmon into small pieces and mix into the sweet potato mixture. Taste and season with salt and pepper.

Form salmon mixture into 8 small patties. Heat 1 tablespoon olive oil in the same pan you cooked the onion mixture over medium-high heat. Add the salmon patties and cook 2-3 minutes per side, until golden brown.

Meanwhile, halve the tomatoes and toss in a medium bowl with the arugula, 1 tablespoon olive oil, a squeeze of lemon, and a pinch of salt and pepper.

Plate a bed of arugula salad and top with the salmon and sweet potato cakes. Finish with a squeeze of lemon and enjoy!