Cook spaghetti according to package directions. Drain.
Meanwhile melt butter in a skillet. Add onion and saute until translucent. Add garlic and red pepper flake and saute 1 more minute. Deglaze the pan with the white wine.
Drain the can of clams into a cup. Whisk the cornstarch into the clam juice from the can. Pour the clam juice mixture into the skillet. Bring to a boil whisking frequently. Let it simmer for about 5 minutes, or until the sauce is reduced and starting to thicken. Mix in the clams and let them heat through, about 1 more minute.
Divide spaghetti between two plates. Top with the arugula and then spoon the clam mixture and all the sauce from the skillet over top. Drizzle with the olive oil and serve with a lemon wedge.
Recipe by Alison's Allspice at https://www.alisonsallspice.com/clam-and-arugula-pasta/