Let some air out of the potato chip bag and then crush the bag with a rolling pin or wine bottle to make fine crumbs. Transfer the potato chip crumbs to a large bowl and add the salmon, ricotta, and Old Bay. Finely grate the zest from the lemon and add it to the bowl (reserve the zested lemon). Stir the mixture well to combine, really breaking up the salmon as you mix.
Divide the mixture into 8 equal portions and use your hands to form each into a patty. It’s helpful to divide the mixture in half and then in half again and so on to make sure the patties are the same size.
Place the butter in a large nonstick skillet over medium-high heat. Once it melts and begins to bubble, place the fish cakes in the skillet and cook without disturbing them until their bottoms are nicely browned (what a sentence!), 2 to 3 minutes.
Use a spatula to carefully flip each one over and cook until nicely browned on the second side, another 2 to 3 minutes. You might need to cook the fish cakes in 2 batches depending on the size of your pan (you don’t want to crowd the pan, and definitely give yourself space to flip them—think of the spacing like pancakes). Transfer the fish cakes to a plate and cover them with foil to keep them warm.
Turn the heat to high and place the peas, half-and-half, and salt in the same skillet. Cook, stirring, just until the peas are bright green and tender and the half-and-half has reduced slightly, about 4 minutes. Transfer the saucy peas to a serving platter and place the fish cakes on top. Cut the zested lemon into wedges and serve the wedges with the fish cakes for squeezing over. Serve immediately.