In a medium bowl, mash hearts of palm until shredded. Add bell pepper, green onion, parsley, lemon zest and juice, shallot, garlic paste, Old Bay, flour, egg, and breadcrumbs. Mix to combine, adding more breadcrumbs if needed to hold shape. Form into small patties.
In a shallow dish, mix breadcrumbs with Parmesan cheese. Dredge polenta slices in the mixture until fully coated.
Heat the griddle to medium-high and add oil. Sauté the “crab” cakes and polenta slices until golden and crispy on both sides.
To serve, layer a polenta patty on the plate, add microgreens, top with a “crab” cake, and drizzle with lemon aioli. Dust with Old Bay and garnish with lemon slices.