All you need is a MANUAL POWER toaster oven (ticky knob, not electronic,) a 120V relay (or 240 for Europe) and a thermistor.
Then you can drive the relay with one pin, and read the thermistor with another pin, and Bob's your uncle.
I imagine a shield would be overkill for that. The sketch to apply a heat-soak-spike-cool temperature curve, and turning it into control for a solid state relay, should be quite simple!
For example: 25A, 280V, driven by 3V in:
https://www.digikey.com/product-detail/en/crydom-co/PF240D25/CC1341-ND/278899
Btw: If you have a toaster oven that can turn off top power and just power the bottom, that will make for the most even heat AFAICT.
Some ovens can just be surgically altered to do that.
I have done toaster oven reflow, and made working boards (using a good stencil) but these days I let the friends at MacroFab make boards for me if they contain any kind of fine-pitch stuff.
They've always done right by me, and when they make a mistake, they fess up and make it right. (Like, turned a LED the wrong way once, and I could send it back to have it re-worked on their dime.)
While it takes 3-4 weeks to make a board, and is not SUPER CHEAP OMG!!! it's also surprisingly affordable given the labor involved, and they don't charge that much more for boards than OSH Park does. (Very roughly: Twice the price, twice the time of OSH park, and you get back a mounted/soldered board ready to go instead of just a bare board!)