Cook polenta: Bring salted water and a splash of olive oil to a boil. Whisk in cornmeal; cook 45–60 minutes, stirring, until thick and smooth.
Chill & cut: Spread polenta in a square pan; chill until firm. Cut into squares and dredge lightly in breadcrumbs or panko.
Fry polenta: Fry in canola oil until golden and crisp. Drain on paper towels; season with salt.
Smelts: Rinse, pat dry, dredge in flour and fry until golden. Drain and season.
Serve: Toss fried smelts with arugula. Plate alongside crispy polenta; serve warm.