Heat oil on medium-high heat in a 1 1/2 quart saucepan. Add onion and saute until softened.
Add cauliflower, carrots, and potatoes; saute for 5 minutes. Add the fresh thyme during the last minute.
Stir in chicken stock and bring to a boil. In a small skillet, heat the butter. Add the Canadian bacon and saute until lightly browned. Add bacon to soup.
Reduce heat to low and cover, simmering until vegetables are tender. Ladle soup into four individual flameproof crocks or bowls.
Top each portion with two bread slices and 1/4 of the cheese. Place under the broiler until cheese is bubbly.
