Combine 3 cups hot water, the chicken broth, cut scallion, ginger, garlic, 1 tablespoon sesame oil and the soy sauce in an Instant Pot. Put on and lock the lid, making sure the steam valve is in the sealing position. Set the pot to pressure-cook on high for 10 minutes. When the time is up, carefully turn the steam valve to the venting position. When the steam is released, turn off the pot and remove the lid.
Meanwhile, put the noodles in a bowl and cover with hot water; stir occasionally until softened, about 15 minutes. Gently separate any clumps, then drain and rinse under cool water. Cut the carrots into thin matchsticks, chop the Canadian bacon and thinly slice the remaining 2 scallions. Drain the tofu and cut into 12 chunks.
Set the Instant Pot to sauté on high. Remove the garlic, ginger and scallion from the pot with a slotted spoon; finely chop and return to the pot. Add the noodles, carrots and Canadian bacon; cook, stirring, until the carrots are just tender, about 3 minutes. Turn off the pot. Stir in the spinach and thinly sliced scallions; season with salt.
Divide the soup among bowls and add 3 tofu chunks to each. Drizzle with the remaining 1 tablespoon sesame oil.