Thinly slice the capsicums. Crush or finely chop the garlic. Tear the kale leaves into small pieces, discarding the stems.
Step 2 — Make miso stock
Put the miso paste, half the tomato paste*, and 125ml (½ cup) boiling water in a heatproof jug and stir to dissolve. Bring a medium saucepan of salted water to the boil for the spaghetti.
Step 3 — Make capsicum sauce
Heat 2 tsp olive oil in a separate medium saucepan over high heat. Cook the capsicum, stirring occasionally, 4-5 mins until charred. Reduce heat to medium. Add the garlic and ½ tsp chilli flakes* and cook, stirring, for 1 min or until fragrant. Add the miso stock and half the tomatoes*. Reduce the heat to low and cook, covered, for 10 mins or until the sauce is reduced.
Step 4 — Cook spaghetti and kale
While the sauce is cooking, add three-quarters of the spaghetti* to the pan of boiling water (if you're tempted to throw in all the spaghetti, just note the dish won't be as saucy). Cook, stirring occasionally, for 10 mins. Add the kale and cook for a further 2 mins or until the spaghetti is al dente. Reserve 60ml (¼ cup) cooking water, then drain the spaghetti and kale.
Step 5 — Make lemon salsa
Meanwhile, very finely chop one-quarter of the lemon*, discarding any seeds. (Both lemon peel and flesh is used; the peel adds a distinctive texture and tartness, but if you're not a fan, simply use lemon zest and juice.) Finely chop the parsley leaves, discarding stems. Combine chopped lemon, parsley and 1½ tbs extra virgin olive oil in a bowl and season with salt and pepper.
Step 6 — Toss spaghetti and serve
Using a stick blender, blend the capsicum sauce until almost smooth (take care when blending as it may spit). Taste, then season with salt and pepper. Add the spaghetti and reserved cooking water and cook, tossing, for 1-2 mins until glossy. Divide the spaghetti among bowls and scatter over the vegan cheddar. Serve with the lemon salsa.