You can do this in slow cooker if it has browning feature (or on stove ) Return back over to slow cooker setting add sauce , milk and basil stir to combine
Cook on low for 4 hours
In the meantime cook past until just al dente
With around 30mins of the cook time left, add tuna and peas and pasta to sauce
Cook the remaining 30mins or until tuna and peas are heated through & pasta isto your liking :)