Layer onions, carrots and mushrooms (if using) in the bowl of a 4 to 6 quart slow cooker.
Season roast with salt and pepper and place on top of vegetables in cooker.
Add undrained tomatoes around the edge and pour wine (or broth) over all. Mix garlic and herbs together and spread evenly over the top of the roast; lay the bacon slices on top.
Cover and cook on HIGH for 1 hour, turn to LOW and cook for 7-8 hours (or cook on LOW for 10 hours).
Instant Pot Instructions
Add onions and drained tomatoes to Instant Pot (Note: do not add carrots and mushrooms here). Place the roast on top, season with salt and pepper, and pour wine or broth over all. Mix the garlic and dried herbs together and spread over roast, then lay the bacon slices on top.
Close the lid, press the "Manual" button and cook on high pressure for 60 minutes (add 15 min to come up to pressure, so it will be about 75 minutes for 3-4 pounds roast).
After the cooking time is complete, press "Cancel" and carefully release the pressure. Once pressure completely releases, open lid and add the the carrots and mushrooms or other vegetables.
Close lid and pressure cook for an additional 10 minutes. When cooking has finished press "Cancel" and release the steam pressure again. (NOTE: the total Instant Pot time with 2 times reaching pressure and 2 releases is 2 hours + the 15 minutes prep.)
Oven Pot Roast Instructions
Heat oven to 350 degrees.
Add onions and undrained tomatoes to a 4 to 6 quart dutch oven or roaster (Note: do not add carrots and mushrooms here). Place the roast on top, season with salt and pepper, and pour wine or broth over all. Mix the garlic and dried herbs together and spread over roast, then lay the bacon slices on top.
Cook, covered, for 2 hours. Remove from oven, add the carrots and mushrooms, cover and return to oven for another hour or until a meat thermometer registers 145 to 150 degrees. (Note: if it looks like it's drying out when you add the vegetables, add 1/2 cup more broth.)
Tip: You can remove the cover the last 15 minutes to see about crisping up the bacon, if you'd like.
To Serve
Transfer roast to a cutting board and slice against the grain. Arrange on a platter with the vegetables and spoon some of the juices over all. Pass the remaining juice at the table.